The present invention relates to a control valve for fuel injection devices for internal combustion engines, preferably Diesel engines, with a valve housing within which at least one piston is displaceable and which comprises stops for the piston.
Today""s internal combustion engines, Diesel engines, in particular, require an injection process consisting of several individual injection actions for a reliable and clean mixture formation within the combustion chamber of the engine. These injection processes are divided into one or more pre-injections, a main injection and, perhaps one or more subsequent injections of the fuel. For producing the pre-injection fuel quantity, a control unit is employed which requires a high-cost electronic control system and which shows energy losses. Frequently, a damper is employed for producing the pre-injection fuel quantity. This damper, however, cannot be fully utilized in each step of the operation and shows severe deviating depending on the operational location. The reason for this is that the switching time of the control hydraulic is too long in the event of small injection quantities due to the design of the control elements and a small pre-injection quantity can, therefore, be produced only with the help of a significant control-technical structural design and expenditure.
Therefore, it is an object of the present invention to provide a control valve of the aforementioned kind such that a small pre-injection quantity of fuel can be produced at all operational locations without a high control-technical structural design and expenditure
This object is solved by the inventive control valve by providing at least one of the stops to be axially adjustable.
With the inventive control valve, at least one of the stops for the piston is axially displaceable. This determines the stroke of the piston and the time period in the respective end positions corresponding to the closed or opened up control valve. Because of the possibility to adjust the stop, the piston stroke can be varied, depending on what the requirements are. Thereby, the smallest injection quantities, particularly for the pre-injection, and, if necessary, also for a subsequent injection, can be precisely controlled in a simple way without negatively affecting the main injection. It is also possible to reduce leakage losses by correspondingly adjusting the position of the stop.